Most electronic packages, which include sensors connected to input/output devices thereof, utilize leadframes, a PCB, or combinations thereof. Such electronic packages generally require that a conductors and/or insulators connect from a sensing element to the outside of the package for a customer to properly interface with the device. Leadframes provide customized configurations in which a designer can create many packages in order to meet a customer's overall need. Unfortunately, all of this customization must link in some electrical means to create a device.
In a typical sensing device, an SOIC may be created to house the die and permit electrical contact for the next operation. In many leadframe designs, the central focus is a “plug”, which is the customer's means of connection to the sensing portion of the device. Common methods of connecting to leadframes including wire bonding and soldering techniques. Both of these connecting methods require that the leadframe be plated. Common plating material for wire bonding involves the use of gold, while tin is often utilized for soldering.
A number of complications are involved in the use of leadframes. For example, leadframes require cleaning following stamping and prior to plating in order to remove excessive oils and contaminates. Leadframes also function as a conductor and require an insulator to allow a usable electronic connection. Leadframes additionally require a significant capital investment to produce the conductor. The ability of a leadframe to be manipulated into a desired package configuration is very limited because the method of production chosen typically involves stamping. The simplest leadframe would be flat and straight. Any deviation from the simple design requires significant effort to ensure that angles and bends are precise for not only the package configuration, but also interface with the overmold process.
The over mold process provides the insulation characteristics for the circuit and also the structure required to hold the leadframe. The cost of the mold is greatly influenced not only by its dimensional configuration, but also by the ability to interface with the leadframe. The interface with the leadframe in the mold may be one of the driving factors of circuit costs, because of the consistency required to ensure repeatability, eliminate flash, and prevent leadframe movement. In such processes, 99.9% of the material required to create the electrical connection is wasted. Waste in such processes is found not only what is thrown away via the stamping process, but also, in what is required to create the leadframe.
Leadframes do not optimize material thickness for electrical properties in sensor devices. The thickness driver focuses on requirements for the plug out configuration in the device and necessary requirements involved in the stamping process. Little leeway exists for the package designer to meet the plug connection requirements of the customer while still optimizing the conductor thickness for the sensor, without creating additional electrical joints or increasingly complicated leadframe configuration processes. For example, a customer may require a 0.032″ thick plug. The electrical requirements of the device mandate only 0.005 thick materials. Thus, the electrical properties involved in a stamping manufacturing process may be impossible to achieve due to stamping constraints, as well as handling complications.
A PCB (Printed Circuit Board) has become an economical means for producing circuitry utilizing copper foil, fiberglass, and resin to create the insulated conductor. This method maximizes the efficiency of the conductor when compared to the leadframe, because the conductor material requirement comes closer to meeting the electrical requirements required by the circuit. Yet, PCB issues include the cost of the board when the size becomes large. In addition, the conductor is merely flat. Also, a requirement exists to provide an interconnect to the PCB in order to interface with the customer's I/O. Due to the standardization of PCBs, the designer must attempt to optimize the area within the panel. Additionally, routing may be required, not only to give the PCB dimensional size, but also to disconnect from the panel. Typically, additional structures are required to not only to hold the PCB in place, but also to maintain the plug.
It can therefore be very difficult to separate leadframes from PCBs, because of the interaction required to configure sensing devices. A unique method of creating conductors for electronic packages is the MID (molded interconnected device) technique. Such a method creates the conductor and the insulator by utilizing two different plastics in which one can be plated, while the second plastic (i.e., the insulator) can be molded over the plateable plastic, creating a pattern for the circuitry.
Unfortunately, such process requires two molds to create the circuitry. The capital investment of such processes is similar to the leadframe method wherein the conductive plastic is inserted into a mold and all the variation of both conductive plastic and the mold from the second plastic must interface precisely. After the over molding process, the package is plated to create the electrical traces required for the circuitry. The precision of such traces is equal to the precision of the mold, which interfaces to plastics. Although the MID technique permits increasingly complicated traces in leadframe designs, a number of issues are related to the MID method.
MID operations typically require two molds, along with a high precision for interfacing the two molds to obtain higher resolution of traces. A great deal of handling is also required to produce the circuitry. MID operations also typically lack automation, which is desirable in order to provide manufacturing ease of assembly.
A second plastic circuitry method utilizes a photomask to develop a circuit. This only requires one mold to produce the substrate. The creation of the other circuitry is accomplished by photo, masking, and etching techniques. This method permits, 3-D circuitry not only for one mold, but also permits the change of the circuitry without changing the plastic substrate configuration. This key flexibility permits multiple circuit configurations to be created from one base package without the complications of additional capital expenditure or process modification. Circuitry is merely altered by providing a new photomask. Another benefit of this process is a high resolution in the trace width.
Issues with this process include lack of automation, and a requirement for handling between processes to create the circuitry. Angles are also required to configure the circuitry in a 3-D mode. Complications can also be encountered when creating multiple parts and a panel assembly, while still maintaining the circuitry resolution that would be seen on a single part in high volumes.